This invention relates to an operation having the object of providing the open mouth zone of a metal can with a constricted end portion.
For this purpose the invention provides a device for forming a constriction on the open end zone of a metal can with a cylindrical body, comprising:
(1) a support member for supporting the bottom of a can and pushing displacement thereof in axial direction; PA1 (2) an annular anvil placed coaxially of this support member, on the side of which facing the support member an internal modelling surface is present which in the direction away from the support member has a form adapted to the desired shape of the constriction; and PA1 (3) a freely-rotating roller having a form adapted to the shape of the modelling surface, which roller can press the end zone of a positioned can forcefully against the modelling surface, which roller is carried by a support member which is driven by drive means in a circular path concentric to the annular modelling surface, wherein the axis of rotation of the freely-rotating roller extends at least approximately in the axial direction.
During use of the device a rolling operation takes place wherein the can for processing is positioned relative to the annular anvil such that the end rim of the can comes to lie against the anvil. The end rim of the can is subsequently pressed forcibly against the anvil by a fully peripheral rolling operation by means of the freely-rotating roller. The shapes of the anvil and the freely-rotating roller are mutually adapted and correspond with the shape of the constriction to be obtained.
A gradual shifting of the can in axial direction takes place during the operation.
The operation is terminated at the moment when the constriction has reached the desired length. The shape is determined by the form of the anvil and the freely-rotating roller.
The freely-rotating roller can have a rotational centre line with the same direction as that of the can. The device can however advantageously have the feature that the rotational axis of the freely-rotating roller lies in a tangential plane and forms a small angle with the axial direction. A very effective ironing is achieved herewith and the material "seeks" a path between the ring and the roller. Thus achieved is that minimal axial forces are exerted on the can wall.
A particular embodiment has the feature that the angle has a value in the order of magnitude of 0.5.degree..
In a practical embodiment the bearing construction for the freely-rotating roller revolves with respect to the fixedly disposed can. This permits a very simple construction. It will be apparent that the complementary arrangement is also possible. What is important here is the relative movement of the roller relative to the can.
The roller and the anvil must be very hard. For an acceptable stand-time use can for instance be made of hard-metal or another material with a very high wear resistance and hardness.
A certain flexibility in the construction can be useful in order to properly position the co-acting surfaces relative to one another under all conditions. Excessive rigidity in the construction can result in extremely great forces which could have an adverse effect on the useful life of the device.